Antihemophilic factor (AHF) of intermediate purity as prepared by the method described in U.S. Pat. No. 3,652,530 has been found to contain about 10 factor VIII units per ml at 20-25 fold purification over plasma. The method of preparation described in U.S. Pat. No. 3,652,530 is based on the extraction of the AHF-containing fraction from cryoprecipitate followed by partial purification with aluminum hydroxide. A product which is more concentrated than that obtained by the method of U.S. Pat. No. 3,652,530 is desirable to facilitate administration of AHF by syringe rather than by infusion, particularly for home treatment of hemophiliacs.
Previous attempts to improve factor VIII potency of the AHF-containing concentrate by reducing the volume of the extracting buffer have resulted in deteriorated filtrability of the AHF solution and decreased solubility of the lyophilized AHF product, presumably because of excessive protein content. This suggests that increased purification is needed in order to permit preparation of a more concentrated, readily soluble AHF product. Highly purified and concentrated AHF has been previously prepared by fractionation with polyethylene glycol, but at the expense of significant AHF losses.
The present invention is concerned with an improved method for increasing the purification and concentration of AHF, based on the principle of fractional extraction. By incorporating a cold extraction step to selectively remove some impurities prior to extraction of AHF from cryoprecipitate, there has been obtained a substantial increase in the purity as well as the potency of AHF without adding any new reagent to the system.
The method of the present invention includes the steps of: (a) cryoprecipitation of plasma; (b) a cold extraction of the cryoprecipitate at low temperature, approximately 0.degree. C, to obtain a cold insoluble fraction having cold soluble impurities removed therefrom; and (c) extraction of the cold insoluble fraction at a temperature of approximately 21.degree. C to obtain a solution containing AHF. The solution containing AHF is then subjected to further treatment including deprothrombinization with aluminum hydroxide gel, stabilization with sodium citrate and filtration, after which the AHF-containing concentrate is recovered by means such as freezing and lyophilization.